Embodiments of the present disclosure generally relate to photo masks used in fabrication of semiconductor devices and, more particularly, to blank masks for extreme ultraviolet (EUV) lithography, methods of fabricating the same, and methods of correcting registration errors thereof.
Semiconductor devices are manufactured using various unit processes such as a deposition process, a lithography process, an etching process, a diffusion process, an impurity implantation process and/or the like. The lithography process may be performed with a photo mask including circuit patterns, and the shapes of the circuit patterns may be transferred onto a wafer during the lithography process. As the semiconductor devices become more highly integrated, sizes of the circuit patterns of the photo mask have been continuously reduced. Thus, there may be some limitations in fabricating the photo masks. In particular, as the semiconductor devices are scaled down to have a minimum feature size of about 30 nanometers or less, there may be still limitations in transferring the fine patterns having line widths of about 30 nanometers or less on a wafer with a lithography apparatus that employs argon fluoride (ArF) lasers generating deep ultraviolet (DUV) rays as light sources. Thus, extreme ultraviolet (EUV) lithography processes have been proposed to overcome the limitations of the lithography process utilizing the deep ultraviolet (DUV) rays.
The EUV lithography processes may use EUV rays having a wave length within the range of about 13.2 nanometers to about 13.8 nanometers, which is shorter than wavelengths of lights generated by KrF lasers or ArF lasers. The EUV rays may be more readily absorbed into most of material layers and may have a refractive index of about one in most of material layers. Thus, it may be difficult to apply refracting optical systems used in the conventional lithography processes with visible rays or general ultraviolet rays to the EUV lithography processes. For the reasons described above, the EUV lithography processes employ reflecting optical systems (also referred to as mirror optical systems), for example, reflection type photo masks and mirrors.
The reflection type photo masks used in the EUV lithography processes may be configured to include a mask substrate and a light reflection layer on the mask substrate. The light reflection layer may include a plurality of molybdenum (Mo) layers and a plurality of silicon (Si) layers which are alternately stacked. That is, the light reflection layer may be a laminated layer. Meanwhile, circuit patterns of the reflection type photo masks may be formed of a light absorption layer, and shapes of the circuit patterns may be transferred onto a wafer. The light absorption layer and the light reflection layer may be formed using an ion beam sputtering technique or a magnetron sputtering technique.
When the light absorption layer and the light reflection layer are formed on the mask substrate, the mask substrate is supported by a supporting member, for example, a mechanical chuck or an electrostatic chuck. The mechanical chuck may cause vibration of the mask substrate during the process for forming the light absorption layer or the light reflection layer. Thus, the electrostatic chuck rather than the mechanical chuck may be widely used as the supporting member. The electrostatic chuck may be used to support the photo mask even when the circuit patterns of the photo mask are formed or the photo mask is handled during the lithography process. Thus, a conductive layer may be formed on a surface of the reflection type photo mask opposite to the circuit patterns and alignment marks to fix the reflection type photo mask on the electrostatic chuck employed in an EUV lithography apparatus. In general, the conductive layer on the reflection type photo mask may include an opaque material blocking lights, for example, a chrome nitride layer, and an entire back side surface of the mask substrate may be cover with the conductive layer.
Recently, high overlay accuracy of the photo masks has been increasingly demanded with reduction of design rules of the semiconductor devices, and improvement of mask registration errors has been continuously required. In the event that an ArF light source is used in a lithography process, the mask registration errors may be corrected by irradiating a laser onto a back side surface of a photo mask to deform a mask substrate (e.g., a quartz substrate). However, in case of the EUV lithography process, it may be difficult to correct the mask registration errors with a method of irradiating a laser onto a back side surface of the reflection type photo mask because the back side surface of the reflection type photo mask is covered with a conductive layer.